Video Transcript
You are in a building when someone
shouts, “Fire!” In response you jump, startled. In this reflex action, what is the
effector?
This question asks us to identify
the effector in a reflex action. You might have heard the term
“reflex” used before, like when a doctor taps your knee during a check-up
appointment or when you jump as something, or someone, scares you. In both of these cases, a reflex is
an unconscious response to a stimulus. A stimulus is a change in the
internal or external environment that brings about a response.
You don’t need to think about the
action for it to happen, since it occurs involuntarily. All changes in the surrounding
environment, and in the internal environment of the body itself, are detected by
receptors. Here they are thermoreceptors in
the skin of the finger that are detecting heat. These receptors then transmit an
electrical signal to sensory neurons which lead to relay neurons in the central
nervous system. This composes the first half of the
reflex arc.
Using the diagram, can you work out
where this signal travels next? It will move from the relay neurons
to motor neurons, which eventually meet with effectors. An effector is the part of a body,
usually a muscle or gland, that carries out a response to a stimulus.
Now that we have discussed some
terminology relating to reflex actions, let’s take another look at our question. We are asked about a situation
involving someone shouting “Fire!,” and you jumping because you are startled. Since the response is automatic, we
consider this a reflex action, and the response to the stimulus involves
jumping. So, the effector must be the
muscles which make you jump. This means that the correct
response to our question “what is the effector?” is the muscles in your leg.
